"Killer" is the last episode of the year not to tie into either the Control or outlaw Travis storylines, partly as it was intended to run earlier in the year (roughly in place of "Horizon"; Gan was added to that episode and had his perfunctory role in this one cut), but it makes for something of a nice buffer anyway despite largely being a standalone. The action takes place on Phosphoron, a planet with a Federation scientific colony, though generally the characters are politically ambivalent - something which fits in with "Trial" as humanising at least some of the Federation. This strengthens the series somewhat in that it shows there are actually people out there worth saving.
Anyone who knows anything about Bob Holmes will tell you he likes a good double-act and as such it's no surprise that this episode (and his second, and the fourth he writes for the last year) centre on Avon and Vila. The pair haven't really been used as a unit up until now, at least not particularly more than any other two crew members have been, but it makes perfect sense. Both have a complementing set of skills, a healthy respect for self-preservation and are happy to go along with Blake while it suits them but would probably jack it all in for a sack of cash and a promise of amnesty. Having them teleport down to Phosphoron gives the early scenes some real zap as both actors seize the opportunity and relish Holmes' habit of giving great dialogue to unconventional heroes. This fine showing probably did a lot to set up the pair's dynamic for Season 3.
Also playing into the show's increased forefronting of Avon is the use of Tynus, an old partner in crime working on Phosphoron as a technician. This adds a bit to Avon's pre-Liberator story and for once seems to ring truer than just being an excuse to introduce an old friend for plotting reasons. It's kept nicely vague as to whether it's the big job Avon got lifted for or a previous heist. It's also good that Tynus is just as untrustworthy as we're led to believe Avon is or was. It actually does Avon's intelligence a little bit that he turns up and treats the guy like shit and is seemingly blindsided to the extent that he has to be saved by the huge contrivance of Tynus writing down his message to the Federation on paper and leaving it in the room with Avon & Vila, the latter then finding it by accident when disposing of some rubbish. Ouch.
The other plot-line concerns Blake teleporting down to a different part of the same facility after an old sleeper ship mysteriously appears. Cally sensing something hostile about it is a bit of a tenuous excuse for Blake to go in alone to warn the scientists, who could well ship him straight to the Federation. Luckily base chief Bellfriar and side-kick Gambrell don't care who he is, which is fun and allows for a nice pair of characterisations but it just seems a reach Blake would do something like that, even allowing for the switched broadcast date removing the trauma of "Pressure Point" from him.
To bear Cally out (not that she does much all episode, the third on the trot with the girls staying on the ship; she does wear a lovely red crushed velvet top that wouldn't look out of place on Marco Pirroni, however) the vessel does include a plague-ridden body (with alien warfare the culprit, an interesting harbinger of the end of the season) and it leads to rather a smashing video nasty plague rampage as the disease rapidly spreads through the complex, complicating Avon & Vila's mission at the same time. Blake hangs around to give his input, which is perhaps a bit strange - if you squint it fits in with his inability to not help someone but really he seems more curious about it all, it's like Holmes accidentally wrote two Avon plotlines in the same episode.
But yeah, it's still fun, and the episode really benefits from Holmes' approach to detail. Little lines and asides give a feel for the way Q-Base runs and makes many of its' personnel feel real - even the doctor doing the autopsy (played by "Tomb of the Cybermen" director Morris Barry, of all people) has a few little tics to his behaviour. And it works because you kind of want them all to pull through; Holmes is a master at this sort of world-building and it makes what could have been a perfunctory episode that bit more memorable. It's all capped by a good dilemma at the end too, where Blake is back on the ship and Phosphoron is dead and full of plague. Servalan (unseen) is on the way and would be traveling to her death but Blake feels that the plague could wipe out mankind and that he owes it to the species to leave a warning beacon. Avon is disgusted by missing this chance to kill her but I think Blake just about does the right thing. Plus he delivers his final justification to Jenna, and her listening to it is the only thing she does all episode.
The other thing that sticks in the mind from this one is dear old Mad Mary Hudson - being made early in the season meant she hadn't spent all the money yet or been wheeled out and the result is the Q-Base personnel have the most batshit gear certainly of the series and maybe ever. Tynus and his fellow technicians (including the disguised Avon and Vila) get these amazing brown lobster carapace type things, the rescue team sent onboard the ship are dressed as the Michelin Man and the fire team seems to be cosplaying as spoons from Beauty and the Beast. But then it's more fun than endless drones in boilersuits I suppose.
Overall it's a weird episode, but in a good way. Holmes doesn't so much write for the B7 format as tweak the format to fit what he wants to write and while some of it might be a little odd it's got two decent plots, a plethora of well-acted, well-written characters, some of the series' most successful horror elements and is generally exciting and engaging for all its' fudges.